This disclosure relates generally to methods and apparatus for generating pulses in a fluid column, as may be used for telemetry between a surface location and downhole instrumentation within a subterranean well.
The use of pulses in a fluid column within tubular members in a wellbore, typically termed “mud pulse telemetry,” is generally well known in the art apart from the particular teachings of this disclosure. Numerous systems have been proposed for generating such pulses in the fluid column, typically broadly referred to as drilling “mud,” though the actual fluid may be any well servicing fluid as known in the art. In accordance with this common terminology in the industry, the fluid pulse generating device will be described as a “mud pulse generator.” With the clear understanding that this term conveys no implication as to the type, nature, or purpose of the fluid in which the pulses are generated.
Various forms of rotating assemblies have been proposed to produce such fluid pulses, including some having a rotor operable to incrementally rotate to open (or relatively partially open), and close (or relatively partially close), flow fluid passageways to periodically restrict or block the flow, thereby causing periods of pressure build up, and thus the pulses as desired for the telemetry. Other known forms of rotating systems include a rotor which rotates generally continually, and wherein the speed of the rotor is varied to facilitate pulses at a momentary selected frequency to execute a desired communication protocol. Still other known systems utilize linearly operating valves, such as poppet valves, to generate the desired pulses. Each of these systems offers various advantages and disadvantages.